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    <title>Image Filters</title>
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          <h4 id="title">Image Filters</h4>
          <div id="map" class="map"></div>
<select id="kernel" name="kernel">
  <option>none</option>
  <option selected>sharpen</option>
  <option value="sharpenless">sharpen less</option>
  <option>blur</option>
  <option>shadow</option>
  <option>emboss</option>
  <option value="edge">edge detect</option>
</select>

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          <p id="shortdesc">Apply a filter to imagery</p>
          <div id="docs"><p>Layer rendering can be manipulated in <code>precompose</code> and <code>postcompose</code> event listeners. These listeners get an event with a reference to the Canvas rendering context. In this example, the <code>postcompose</code> listener applies a filter to the image data.</p>
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          <div id="api-links">Related API documentation: <ul class="inline"><li><a href="../apidoc/ol.Map.html" title="API documentation for ol.Map">ol.Map</a></li>,<li><a href="../apidoc/ol.View.html" title="API documentation for ol.View">ol.View</a></li>,<li><a href="../apidoc/ol.layer.Tile.html" title="API documentation for ol.layer.Tile">ol.layer.Tile</a></li>,<li><a href="../apidoc/ol.proj.html" title="API documentation for ol.proj">ol.proj</a></li>,<li><a href="../apidoc/ol.source.BingMaps.html" title="API documentation for ol.source.BingMaps">ol.source.BingMaps</a></li></ul></div>
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        <form method="POST" id="jsfiddle-form" target="_blank" action="https://jsfiddle.net/api/post/library/pure/">
          <textarea class="hidden" name="js">var key &#x3D; &#x27;Your Bing Maps Key from http://www.bingmapsportal.com/ here&#x27;;

var imagery &#x3D; new ol.layer.Tile({
  source: new ol.source.BingMaps({key: key, imagerySet: &#x27;Aerial&#x27;})
});

var map &#x3D; new ol.Map({
  layers: [imagery],
  target: &#x27;map&#x27;,
  view: new ol.View({
    center: ol.proj.fromLonLat([-120, 50]),
    zoom: 6
  })
});

var kernels &#x3D; {
  none: [
    0, 0, 0,
    0, 1, 0,
    0, 0, 0
  ],
  sharpen: [
    0, -1, 0,
    -1, 5, -1,
    0, -1, 0
  ],
  sharpenless: [
    0, -1, 0,
    -1, 10, -1,
    0, -1, 0
  ],
  blur: [
    1, 1, 1,
    1, 1, 1,
    1, 1, 1
  ],
  shadow: [
    1, 2, 1,
    0, 1, 0,
    -1, -2, -1
  ],
  emboss: [
    -2, 1, 0,
    -1, 1, 1,
    0, 1, 2
  ],
  edge: [
    0, 1, 0,
    1, -4, 1,
    0, 1, 0
  ]
};

function normalize(kernel) {
  var len &#x3D; kernel.length;
  var normal &#x3D; new Array(len);
  var i, sum &#x3D; 0;
  for (i &#x3D; 0; i &lt; len; ++i) {
    sum +&#x3D; kernel[i];
  }
  if (sum &lt;&#x3D; 0) {
    normal.normalized &#x3D; false;
    sum &#x3D; 1;
  } else {
    normal.normalized &#x3D; true;
  }
  for (i &#x3D; 0; i &lt; len; ++i) {
    normal[i] &#x3D; kernel[i] / sum;
  }
  return normal;
}

var select &#x3D; document.getElementById(&#x27;kernel&#x27;);
var selectedKernel &#x3D; normalize(kernels[select.value]);


/**
 * Update the kernel and re-render on change.
 */
select.onchange &#x3D; function() {
  selectedKernel &#x3D; normalize(kernels[select.value]);
  map.render();
};


/**
 * Apply a filter on &quot;postcompose&quot; events.
 */
imagery.on(&#x27;postcompose&#x27;, function(event) {
  convolve(event.context, selectedKernel);
});


/**
 * Apply a convolution kernel to canvas.  This works for any size kernel, but
 * performance starts degrading above 3 x 3.
 * @param {CanvasRenderingContext2D} context Canvas 2d context.
 * @param {Array.&lt;number&gt;} kernel Kernel.
 */
function convolve(context, kernel) {
  var canvas &#x3D; context.canvas;
  var width &#x3D; canvas.width;
  var height &#x3D; canvas.height;

  var size &#x3D; Math.sqrt(kernel.length);
  var half &#x3D; Math.floor(size / 2);

  var inputData &#x3D; context.getImageData(0, 0, width, height).data;

  var output &#x3D; context.createImageData(width, height);
  var outputData &#x3D; output.data;

  for (var pixelY &#x3D; 0; pixelY &lt; height; ++pixelY) {
    var pixelsAbove &#x3D; pixelY * width;
    for (var pixelX &#x3D; 0; pixelX &lt; width; ++pixelX) {
      var r &#x3D; 0, g &#x3D; 0, b &#x3D; 0, a &#x3D; 0;
      for (var kernelY &#x3D; 0; kernelY &lt; size; ++kernelY) {
        for (var kernelX &#x3D; 0; kernelX &lt; size; ++kernelX) {
          var weight &#x3D; kernel[kernelY * size + kernelX];
          var neighborY &#x3D; Math.min(
              height - 1, Math.max(0, pixelY + kernelY - half));
          var neighborX &#x3D; Math.min(
              width - 1, Math.max(0, pixelX + kernelX - half));
          var inputIndex &#x3D; (neighborY * width + neighborX) * 4;
          r +&#x3D; inputData[inputIndex] * weight;
          g +&#x3D; inputData[inputIndex + 1] * weight;
          b +&#x3D; inputData[inputIndex + 2] * weight;
          a +&#x3D; inputData[inputIndex + 3] * weight;
        }
      }
      var outputIndex &#x3D; (pixelsAbove + pixelX) * 4;
      outputData[outputIndex] &#x3D; r;
      outputData[outputIndex + 1] &#x3D; g;
      outputData[outputIndex + 2] &#x3D; b;
      outputData[outputIndex + 3] &#x3D; kernel.normalized ? a : 255;
    }
  }
  context.putImageData(output, 0, 0);
}
</textarea>
          <textarea class="hidden" name="css"></textarea>
          <textarea class="hidden" name="html">&lt;div id&#x3D;&quot;map&quot; class&#x3D;&quot;map&quot;&gt;&lt;/div&gt;
&lt;select id&#x3D;&quot;kernel&quot; name&#x3D;&quot;kernel&quot;&gt;
  &lt;option&gt;none&lt;/option&gt;
  &lt;option selected&gt;sharpen&lt;/option&gt;
  &lt;option value&#x3D;&quot;sharpenless&quot;&gt;sharpen less&lt;/option&gt;
  &lt;option&gt;blur&lt;/option&gt;
  &lt;option&gt;shadow&lt;/option&gt;
  &lt;option&gt;emboss&lt;/option&gt;
  &lt;option value&#x3D;&quot;edge&quot;&gt;edge detect&lt;/option&gt;
&lt;/select&gt;
</textarea>
          <input type="hidden" name="wrap" value="l">
          <input type="hidden" name="resources" value="https://openlayers.org/en/v3.20.0/css/ol.css,https://openlayers.org/en/v3.20.0/build/ol.js">
        </form>
        <pre><code id="example-source" class="language-markup">&lt;!DOCTYPE html&gt;
&lt;html&gt;
  &lt;head&gt;
    &lt;title&gt;Image Filters&lt;/title&gt;
    &lt;link rel="stylesheet" href="https://openlayers.org/en/v3.20.0/css/ol.css" type="text/css"&gt;
    &lt;!-- The line below is only needed for old environments like Internet Explorer and Android 4.x --&gt;
    &lt;script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"&gt;&lt;/script&gt;
    &lt;script src="https://openlayers.org/en/v3.20.0/build/ol.js"&gt;&lt;/script&gt;
  &lt;/head&gt;
  &lt;body&gt;
    &lt;div id&#x3D;&quot;map&quot; class&#x3D;&quot;map&quot;&gt;&lt;/div&gt;
    &lt;select id&#x3D;&quot;kernel&quot; name&#x3D;&quot;kernel&quot;&gt;
      &lt;option&gt;none&lt;/option&gt;
      &lt;option selected&gt;sharpen&lt;/option&gt;
      &lt;option value&#x3D;&quot;sharpenless&quot;&gt;sharpen less&lt;/option&gt;
      &lt;option&gt;blur&lt;/option&gt;
      &lt;option&gt;shadow&lt;/option&gt;
      &lt;option&gt;emboss&lt;/option&gt;
      &lt;option value&#x3D;&quot;edge&quot;&gt;edge detect&lt;/option&gt;
    &lt;/select&gt;
    &lt;script&gt;
      var key &#x3D; &#x27;Your Bing Maps Key from http://www.bingmapsportal.com/ here&#x27;;

      var imagery &#x3D; new ol.layer.Tile({
        source: new ol.source.BingMaps({key: key, imagerySet: &#x27;Aerial&#x27;})
      });

      var map &#x3D; new ol.Map({
        layers: [imagery],
        target: &#x27;map&#x27;,
        view: new ol.View({
          center: ol.proj.fromLonLat([-120, 50]),
          zoom: 6
        })
      });

      var kernels &#x3D; {
        none: [
          0, 0, 0,
          0, 1, 0,
          0, 0, 0
        ],
        sharpen: [
          0, -1, 0,
          -1, 5, -1,
          0, -1, 0
        ],
        sharpenless: [
          0, -1, 0,
          -1, 10, -1,
          0, -1, 0
        ],
        blur: [
          1, 1, 1,
          1, 1, 1,
          1, 1, 1
        ],
        shadow: [
          1, 2, 1,
          0, 1, 0,
          -1, -2, -1
        ],
        emboss: [
          -2, 1, 0,
          -1, 1, 1,
          0, 1, 2
        ],
        edge: [
          0, 1, 0,
          1, -4, 1,
          0, 1, 0
        ]
      };

      function normalize(kernel) {
        var len &#x3D; kernel.length;
        var normal &#x3D; new Array(len);
        var i, sum &#x3D; 0;
        for (i &#x3D; 0; i &lt; len; ++i) {
          sum +&#x3D; kernel[i];
        }
        if (sum &lt;&#x3D; 0) {
          normal.normalized &#x3D; false;
          sum &#x3D; 1;
        } else {
          normal.normalized &#x3D; true;
        }
        for (i &#x3D; 0; i &lt; len; ++i) {
          normal[i] &#x3D; kernel[i] / sum;
        }
        return normal;
      }

      var select &#x3D; document.getElementById(&#x27;kernel&#x27;);
      var selectedKernel &#x3D; normalize(kernels[select.value]);


      /**
       * Update the kernel and re-render on change.
       */
      select.onchange &#x3D; function() {
        selectedKernel &#x3D; normalize(kernels[select.value]);
        map.render();
      };


      /**
       * Apply a filter on &quot;postcompose&quot; events.
       */
      imagery.on(&#x27;postcompose&#x27;, function(event) {
        convolve(event.context, selectedKernel);
      });


      /**
       * Apply a convolution kernel to canvas.  This works for any size kernel, but
       * performance starts degrading above 3 x 3.
       * @param {CanvasRenderingContext2D} context Canvas 2d context.
       * @param {Array.&lt;number&gt;} kernel Kernel.
       */
      function convolve(context, kernel) {
        var canvas &#x3D; context.canvas;
        var width &#x3D; canvas.width;
        var height &#x3D; canvas.height;

        var size &#x3D; Math.sqrt(kernel.length);
        var half &#x3D; Math.floor(size / 2);

        var inputData &#x3D; context.getImageData(0, 0, width, height).data;

        var output &#x3D; context.createImageData(width, height);
        var outputData &#x3D; output.data;

        for (var pixelY &#x3D; 0; pixelY &lt; height; ++pixelY) {
          var pixelsAbove &#x3D; pixelY * width;
          for (var pixelX &#x3D; 0; pixelX &lt; width; ++pixelX) {
            var r &#x3D; 0, g &#x3D; 0, b &#x3D; 0, a &#x3D; 0;
            for (var kernelY &#x3D; 0; kernelY &lt; size; ++kernelY) {
              for (var kernelX &#x3D; 0; kernelX &lt; size; ++kernelX) {
                var weight &#x3D; kernel[kernelY * size + kernelX];
                var neighborY &#x3D; Math.min(
                    height - 1, Math.max(0, pixelY + kernelY - half));
                var neighborX &#x3D; Math.min(
                    width - 1, Math.max(0, pixelX + kernelX - half));
                var inputIndex &#x3D; (neighborY * width + neighborX) * 4;
                r +&#x3D; inputData[inputIndex] * weight;
                g +&#x3D; inputData[inputIndex + 1] * weight;
                b +&#x3D; inputData[inputIndex + 2] * weight;
                a +&#x3D; inputData[inputIndex + 3] * weight;
              }
            }
            var outputIndex &#x3D; (pixelsAbove + pixelX) * 4;
            outputData[outputIndex] &#x3D; r;
            outputData[outputIndex + 1] &#x3D; g;
            outputData[outputIndex + 2] &#x3D; b;
            outputData[outputIndex + 3] &#x3D; kernel.normalized ? a : 255;
          }
        }
        context.putImageData(output, 0, 0);
      }
    &lt;/script&gt;
  &lt;/body&gt;
&lt;/html&gt;</code></pre>
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